The present invention relates to a side airbag device that absorbs impacts applied to a side of a vehicle to protect an occupant.
For example, Japanese Laid-Open Patent Publication No. 2000-280853 discloses a side airbag apparatus having a side airbag. The interior of the side airbag is divided by a partition into a rear deployment zone and a front deployment zone. A part of the side airbag that corresponds to the rear deployment zone is inflated in a position rearward of an arm of an occupant. A part of the side airbag that corresponds to the front deployment zone contacts an arm of the occupant when inflated. The part of the side airbag corresponding to the rear deployment zone is immediately deployed and inflated with gas generated by an inflator of the side airbag apparatus. Thereafter, the part of the side airbag corresponding to the front deployment zone is deployed and inflated.
The entire side airbag is deployed and inflated at the same internal pressure and in the same manner. Therefore, when an occupant presses himself against the side airbag, the internal pressure of the side airbag is increased according to the degree of the pressing. Accordingly, the reaction force applied to the occupant by the side airbag is increased.
Some side airbags have a vent hole to discharge excessive portion of gas supplied by the inflator to the outside of the side airbag. In an initial stage of restraint of an occupant by such a side airbag, the pressure in the side airbag is less than a case where no vent hole is provided as shown by broken line C1, which represents the characteristics of such a side airbag. This is because gas is discharged to the outside from the side airbag through the vent hole. Therefore, to adjust the reaction force that acts on an occupant to a predetermined value in an initial stage of restraint of an occupant, either the output of the inflator needs to be increased or the capacity of the airbag needs to be reduced.